Algodoo

Q, W, and E fire different SAM missiles. Once a missile gets very close to an aircraft, press 1, 2, or 3 to fire shotgun bullets from the missiles. Aim the site using the arrow keys

I tip on shooting. While aiming at the aircraft, make sure to follow through and match the speed of the aircraft with the "laser sight".
If the speed is matched, the missile will hit exactly where you were aiming on the aircraft.

In all fairness to the planes, you dont need the shotgun bullets. the missile itself does enough damage on its own. but if your aim is slightly off, the spread bullets can be helpful.
the numbers correspond to each letter. Q-1, W-2, E-3

(Disclaimer: This gun does not shoot SAM Sites. XD)